1. Field of the Invention
The present invention relates to a recording medium with optical waveguides, and a player which employs the same for guiding a light beam to the optical waveguides, causing reflected part of the guided beam to interfere with a reference light beam for detecting the result, and reproducing recorded information as a time-series signal waveform, which player may also be referred to as a recorded-information reproducing apparatus.
2. Description of the related Art
A conventional optical recording medium, such as an optical disk, is constituted as shown in FIG. 1. This optical recording medium 100 is designed such that with a recording medium as a substrate, recesses 101 (pit recording portions) of low light reflectance, recorded on the substrate surface, and flat portions 102 of high light reflectance are aligned, so that reproduction may be performed while moving the recording medium in the direction of the arrow 103. The ratio of the reflectance of light from the flat portions 102 to that from the recesses 101 is as high as 1:0.3 to 0.5, the signal to noise (S/N) ratio of light intensity is not good enough, and it is difficult to improve the S/N ratio. According to this recording medium 100, a semiconductor laser beam is irradiated in converged manner on each recess 101 or each flat portion 102 for reading them out and then the reflected light is detected, so that a time-series signal may be reproduced only by moving the pit-recorded portions on the recording medium 100. The moving speed of the thus constituted recording medium 100 restricts the access time for reproduction as well as recording, making it difficult to realize high-speed access. Because reproduction or read-out depends on the light reflected from the flat portions, the surface density of the pit-recorded portions is limited, making it quite impossible to provide a three-dimensional lamination.
As shown in FIG. 2, a conventional recorded-information reproducing apparatus, which reproduces information recorded on an optical disk 24 designed as described above, comprises a semiconductor laser 11, lenses 12 to 15, a focus lens 16 mounted on a focus actuator, half mirrors 17 and 18, a 1/2-wavelength plate 19, a wave-shaping prism 20, photo sensors 21 to 23, and a beam splutter 25 constituted of a prism.
The light from the semiconductor 11 passes through the lens 12, wave-shaping prism 20, half mirror 17 and focus lens 16 to enter the recording medium 24. The reflected light from the recording medium 24 is then detected for reproduction of the recorded information.
If the optical disk 24 is a recording medium, such as a pit-formed recording medium or phase-change type recording medium, on which information is recorded as a change in refractive index caused by minute recording portions, the reflected light from the optical disk 24 is detected by the photo detector 21.
If, on the other hand, the optical disk 24 is a recording medium, like a photo-electromagnetic disk, on which information is recorded in the form of presence/absence of magnetic inversion, light reflected from the magnetism inverting recording portions of a minute area and having its deflection plane rotated is separated by the prism beam splitter 25 serving as an analyzer, and then the separated lights are respectively detected by the photo detectors 22 and 23.
At the time of information reproduction by this reproducing apparatus, to cause the optical pickup of the apparatus to follow up the surface vibration of the optical disk 24, the focus lens 16 and the like are moved along the optical axis in accordance with a focus error signal for focusing.
The conventional system has the following shortcomings:
(i) Since a light reflection system involving minute recording portions, such as pits, the light beam needs to be focused for every single recording portion on the recording medium. This impairs the S/N ratio of an optical signal and the amplitude modulation, thus reducing the reliability.
(ii) Since reproduction depends on reflection from the minute recording portions recorded on flat portions, the surface density of the recording portions is limited, making it impossible to ensure three-dimensional lamination.
(iii) Since an optical signal is reproduced for every single recording portion on the recording medium, a time-series signal is reproduced only by the movement of the recording medium. Therefore, the moving speed of the recording medium restricts the cycle period.